Femtosecond laser induced damage threshold and incubation in l-threonine aminoacid crystal

Abstract

l-threonine aminoacid crystals exhibit high second-order optical nonlinearities that can be exploited for second harmonic generation, optical parametric amplification, and optical parametric oscillation. In addition, it possesses a large transparency window and low refractive index, making them an attractive material for photonics devices. Among several processing methods used to develop photonic integrated micro-devices, fs-laser micromachining has stood out for its high resolution, either on the surface or in the bulk, as well as to its flexibility to be used with various types of materials. Although organic crystals present relevant linear and nonlinear optical features, studies on fs-laser processing in such materials are yet scarce. Thus, this work presents a study of the fs-laser incubation and damage threshold fluence determination in l-threonine crystals at 515 nm and 1030 nm. The damage threshold fluence was determined for one up to 10⁵ pulses. For the single pulse regime, we obtained F_th = (0.94 ± 0.04) J/cm² at 1030 nm and F_th = (0.31 ± 0.01) J/cm² at 515 nm. Such difference is explained by the number of photons involved in each case; 5-photons at 1030 nm and 3-photons at 515 nm. Also, a slower incubation dynamic was observed at 515 nm. Still, micro-Raman spectroscopy revealed that no structural modifications were induced by the fs-laser pulses on the sample upon micromachining. Such results provide relevant data for the processing of l-threonine crystals via fs-laser micromachining to achieve organic photonic integrated devices.